This Application is related to an Application entitled, xe2x80x9cImproved Human Interface for Wireless Telephone Stationsxe2x80x9d, being filed concurrently by the same inventor, and being assigned to the same Assignee.
This invention relates to the utilization of traffic channels in a cellular wireless telecommunications system.
In a cellular wireless telecommunications system, the final stage of a connection to a mobile station (MS) involves the use of a radio channel, a traffic (voice or data) channel from a base station, connected to a host controller such as a mobile switching center (MSC). The number of traffic channels available from any base station is limited by a number of factors dependent upon the specific radio technology used and the allotted bandwidth of the base station. In some cases, if all the traffic channels at a preferred base station capable of receiving the signal from the MS are occupied, an alternate base station having available channels can serve the call. However, if this is not the case, the call cannot be set up, and is effectively blocked.
Mobile stations also communicate with their host controller, such as a controlling mobile switching center (MSC) by a control radio channel, which is available even if no voice radio channels are available. Thus, it is possible to signal a mobile station to inform it that it cannot originate a call because no traffic channels are available.
Even though in many or most cases, the number of traffic channels available is adequate for handling the required traffic, there are cases in which sudden peaks of traffic exceed the capabilities of the radio system. For example, if a large airplane lands at an airport, many of the passengers immediately try to make a cellular call, (in part because the pay telephones are also busy). Under those circumstances, if a particular mobile station cannot get a traffic channel, the mobile station keeps sending set-up messages (typically when the user presses the end and then the send buttons), thus flooding the MSC with an excessive number of requests, and possibly creating processing load problems for the MSC.
A problem with the prior art, therefore, is that there is no way of smoothing the traffic load if the number of radio channels is inadequate at a particular time.
While queuing for a traffic channel is one important problem, a similar class of problems exits for queuing for a call transmission resource, such as a trunk in a public network. Queuing for trunks is known for private networks, such as those used to complete 800 calls for companies that have a plurality of automatic call distributors in geographically diverse locations and that queue calls for completion to one of these distributors. However, there is no known arrangement for queuing calls in a public network.
Applicants have carefully studied this problem, and have recognized that the number of traffic channels available in most cellular systems for accessing a particular mobile station is generally large. If all of these traffic channels are busy, the likelihood that one will become available in a short time, or even that a small number of traffic channels will become available in a short time, is substantial. Therefore, in accordance with Applicants"" invention, when no traffic channels are available, a limited number of mobile stations can be queued up for outgoing calls, and/or a limited number of incoming calls can be queued up for completion to idle mobile stations that are currently inaccessible because of the unavailability of a traffic channel.
In accordance with Applicants"" invention, if a call set-up message is received by a host controller such as a mobile switching center (MSC) and no traffic channel is available, the MSC tests whether the expected delay until a traffic channel becomes available is less than some parameter, say N seconds; if not, then the mobile station is informed of the unavailability of radio channels in accordance with the principles of the prior art. If a channel is expected to be available in less than N seconds, the MSC simply waits and tries to set up a connection to the MS when a channel becomes available. If the elapsed time exceeds M seconds and no traffic channel has become available, the caller is notified and, effectively, has the choice of either waiting longer until a traffic channel is available, or disconnecting and abandoning the call. The notification of the caller can be made by a message sent over the control channel which, in the MS, results in a displayed message; or the generation of a tone or a tone cadence; or inventively, in the generation of a message for triggering an announcement. The latter choice has the advantage over a display, because the caller will probably have the MS up to his/her ear, and therefore will not see the display.
In accordance with Applicants"" invention, incoming calls can also be queued up. If an incoming call is received when no traffic channels are available to the called MS, then a test is performed to determine whether the expected wait time before a traffic channel becomes available is less than N seconds. If not, the caller receives an xe2x80x9call radio channels busyxe2x80x9d indication, as in the prior art. If the expected wait time is less than N seconds, then the MSC waits for an available traffic channel. If the waiting time exceeds M seconds, then a pre-recorded announcement, display message, or tone is sent to the caller indicating that the network expects to be able to complete the call shortly, or in approximately P seconds. If the caller does not disconnect, the connection to the called MS is established when a traffic channel becomes available. If the caller disconnects, the call is abandoned.
Advantageously, this arrangement allows for a significant decrease in the number of calls blocked because of unavailability of a traffic channel. Advantageously, this type of arrangement for outgoing calls may significantly alleviate the problem of callers repeatedly sending set-up messages when no traffic channels are available.
For other applications, such as routing long distance calls through a network when a call is initially blocked because no trunk is available for one link of the call, the same queuing arrangement can be used to queue calls waiting for the availability of a trunk. Advantageously, this arrangement can be used to reduce blocking during periods of heavy traffic.